# Accuracy Analysis of GNSS Hourly Ultra-Rapid Orbit and Clock Products from SHAO AC of iGMAS

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## Abstract

**:**

## 1. Introduction

## 2. Data, Methods, and Strategy

## 3. Assessment and Analysis

#### 3.1. Computational Efficiency

#### 3.2. Accuracy Analysis of Different Methods for Orbit Prediction

#### 3.3. Assessment of 6H and 1H Orbit Products

#### 3.4. Assessment of 6H and 1H Clock Products

## 4. Summary and Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A. The POD Processing by Combined Serial and Parallel Threads (CSPT)

## References

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**Figure 1.**Distribution of the global tracking stations used to generate hourly ultra-rapid orbit and clock global navigation satellite system (GNSS) products. The blue circles represent the stations, which can track American Global Positioning System (GPS) satellites; the green circles represent the stations tracking Ruassian Global’naya Navigatsionnaya Sputnikova Sistema (GLONASS); the yellow circles represent the stations tracking European Union’s Galileo, and the red circles represent the stations tracking Chinese BeiDou navigation satellite system (BDS) satellites.

**Figure 3.**Data processing flow chart of the combined serial and parallel threads (CSPT) method for hourly orbit and clock products.

**Figure 4.**Computational efficiency of 6H and 1H products for GPS/GLONASS/Galileo/BDS. The 6H and 1H are on behalf of 6-hourly and 1-hourly products, respectively.

**Figure 5.**Average root mean square (RMS) in along, cross, and radial directions of differences between 6-hourlyorbit products generated by the new and old method and IGS/MGEX final products for 24-h observation session and the 1st–8th hour prediction session.

**Figure 6.**Average RMS of 6-hourly GNSS ultra-rapid orbit products with respect to IGS/MGEX final products for 24-h observation session and 1st–8th prediction session. (

**a**) shows RMS of the MEO orbit for GPS/GLONASS/Galileo, and MEO/IGSO orbit for BDS, (

**b**) displays RMS of GEO orbit for BDS for the observation session and prediction session.

**Figure 7.**Average RMS of 1-hourly GNSS ultra-rapid orbit products with respect to IGS/MGEX final products for 24-h observation session and 1st–2nd prediction session. (

**a**) shows RMS of the MEO orbit for GPS/GLONASS/Galileo, and MEO/IGSO for BDS, (

**b**) displays RMS of GEO orbit for BDS for the observation session and prediction session.

**Figure 8.**Average SD of 6-hourly (

**a**) and 1-hourly (

**b**) GNSS clock versus reference products from IGS/MGEX.

**Figure 9.**Average RMS of 6-hourly (

**a**) and 1-hourly (

**b**) GNSS clock versus reference products from IGS/MGEX.

GPS | GLONASS | Galileo | BDS | |

Thread | GPS | GLONASS+GPS | Galileo+GPS | BDS+GPS |

Undifferenced ionosphere-free combination | GPS: L1,L2 | GLONASS: L1,L2 | Galileo: E1,E5a | BDS: B1,B2 |

GPS: L1,L2 | GPS: L1,L2 | GPS: L1,L2 | ||

Elevation angle cutoff | 7 degrees | |||

Sampling interval | 450 s for 6-hourly updated products | |||

600 s for 1-hourly updated products | ||||

ISB/IFB | Estimated as constant | |||

Satellite clock error | Estimate every sampling interval relative to reference clock | |||

Receiver clock error | Estimate every sampling interval relative to reference clock | |||

A receiver clock fixed as a time reference (such as ALGO, PTBB, WTZR, NRC1, PIE1, ONSA) | ||||

Orbits | Estimated with 5 parameters for solar radiation pressure modeling | |||

station displacement | Solid earth tide, pole tide, ocean tide loading | |||

Earth gravity | EGM 12X12 | |||

RHC phase rotation correction | Phase wind-up applied | |||

Ambiguities | Fixed | |||

Satellite phase center corrections | igs14.atx from IGS | PCO/PCV for BDS-2 [14] | ||

Station phase center corrections | igs14_absolute.atx from IGS | |||

Tropospheric delay | Initial ZTD model: Saastamoinen model | |||

Mapping function: GMF | ||||

Interval: 1-h for ZTD, 12-h for gradient | ||||

ERP | Initial value: downloaded from IERS rapid solution | |||

Constrain: strong constrain | ||||

Reference frame | ITRF 2014 |

Session | GPS | GLONASS | Galileo | BDS | |||
---|---|---|---|---|---|---|---|

MEO | MEO | MEO | MEO | IGSO | GEO | ||

Observation session | 24 h | 0% | 0% | 0% | 0% | 0% | 0% |

Prediction session | 1st hour | 0% | 15% | 12% | 20% | 54% | −7% |

2nd hour | 9% | 14% | 28% | 32% | 59% | −7% | |

3rd hour | 9% | 13% | 41% | 46% | 64% | −6% | |

4th hour | 9% | 15% | 49% | 58% | 69% | −3% | |

5th hour | 13% | 14% | 57% | 69% | 73% | 3% | |

6th hour | 16% | 16% | 64% | 74% | 77% | 9% | |

7th hour | 22% | 18% | 67% | 76% | 80% | 15% | |

8th hour | 32% | 19% | 67% | 73% | 83% | 21% |

Session | GPS | GLONASS | Galileo | BDS–MEO | BDS–IGSO | BDS–GEO |
---|---|---|---|---|---|---|

MEO | MEO | MEO | MEO | IGSO | GEO | |

Observation | 1% | 31% | 13% | 11% | 23% | 9% |

Prediction | 18% | 43% | 45% | 34% | 53% | 15% |

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**MDPI and ACS Style**

Chen, Q.; Song, S.; Zhou, W.
Accuracy Analysis of GNSS Hourly Ultra-Rapid Orbit and Clock Products from SHAO AC of iGMAS. *Remote Sens.* **2021**, *13*, 1022.
https://doi.org/10.3390/rs13051022

**AMA Style**

Chen Q, Song S, Zhou W.
Accuracy Analysis of GNSS Hourly Ultra-Rapid Orbit and Clock Products from SHAO AC of iGMAS. *Remote Sensing*. 2021; 13(5):1022.
https://doi.org/10.3390/rs13051022

**Chicago/Turabian Style**

Chen, Qinming, Shuli Song, and Weili Zhou.
2021. "Accuracy Analysis of GNSS Hourly Ultra-Rapid Orbit and Clock Products from SHAO AC of iGMAS" *Remote Sensing* 13, no. 5: 1022.
https://doi.org/10.3390/rs13051022